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Being overweight is one thing, but where your body fat is stored may make more of a difference to your health. Researchers in Germany report that even among people who are normal weight, having excess fat around the abdomen  being apple-shaped, that is  can increase the risk of premature death.

Dr. Tobias Pischon, an epidemiologist and physician at the German Institute of Human Nutrition in Potsdam, analyzed data collected in a large European database of subjects. Among 359,000 subjects who were followed for nearly 10 years, those with the largest waist measurements, 40.4 inches or greater for men and 35.0 inches or more for women, were twice as likely to die prematurely than those with smaller waists, less than 33.8 inches for men and 27.6 inches for women. By the end of the study, 4,232 of the largest waisted people had died of various causes, from heart disease to cancer and other ailments, while 2,155 of the smallest waisted people had died in the same period. Most surprising was that the association applied even to men and women who were not overweight: People with bigger waists had a greater risk of early death. (See TIME's A-Z Health Guide.)

Current obesity guidelines rely on the body mass index (BMI), a ratio of height and weight. The problem, as many experts have noted, is that the weight component does not distinguish between fat and muscle mass nor does it account for how fat distributed. Recent research suggests that the fat that accumulates around the midsection  and deep in the body around the organs  is more likely to contribute to conditions such as heart disease and diabetes, since it is more metabolically active. Known as visceral fat, these adipose cells tend to secrete hormones and cytokines that can throw the body's energy and biochemical balance off kilter; subcutaneous fat, on the other hand, which rests just under the skin in other parts of the body, is more inert, serving mostly as an energy sink.

Pischon's study highlights the growing importance of measuring the amount of the more active visceral fat, and as the results suggest, waist circumference can be an effective marker and a good predictor of how dangerous that fat can be. "What this study shows is that it is not sufficient to simply rely on BMI," says Pischon. "Waist circumference can even be related to higher mortality in normal weight individuals."

But the difficulty with waist circumference is that so far, the data do not point to a threshold at which health risks shoot up. That means that unlike BMI, which gives people a "normal" or healthy range to adhere to, there is no ideal waist measurement. The study found that waist circumference and risk of death increased linearly, meaning that at any given weight, those with greater waist measurements were at greater risk of dying than those with smaller waists. Pischon's team calculated that for every 5 cm (about 2 inches) increase in girth, the risk of dying increased by 17% for men and by 13% for women. "There is no goal waist circumference, and that is the difficult thing," acknowledges Pischon. "All we can say is that it's always good to have a low waist circumference."

Much still needs to be worked out about how waist circumference is contributing to the greater risk of death  in addition to simply adding visceral fat, says Dr. Franciso Lopez-Jiminez, director of clinical practice and preventive cardiology at the Mayo Clinic, greater waist circumference generally also indicates a greater burden of fat overall, which is a big contributor to heart disease and other metabolic conditions that can lead to early death. "The take-home message from this study is that clinicians need to start measuring waist circumference more and more," he says. "It is rarely measured in clinical practice."